The present invention relates to an optical system unit for optical transceiver and particularly an optical system unit for optical transceiver arranged of receptacle type for coupling with a plurality of optical fibers and transmitting and receiving optical signal over the optical fibers.
It is contemplated that an optical system unit for optical transceiver for coupling with a plurality of optical fibers and transmitting and receiving optical signals over the optical fibers is equivalent to a connection hub (a cable coupler) for coupling a group of LAN (local area network) cables for a local network such as in an office.
Any LAN cable for transmission of electric signals can be joined at one end to a relatively smaller connector and also can transmit and receive a signal over a single line. Accordingly, the hub for coupling the LAN cables for electric signals is common available of a compact size.
On the contrary, a conventional optical system unit for optical transceiver is designed having a desired number of connectors, each connector joined with a fiber optic cable accommodating a transmission optical fiber and a fiber optic cable accommodating a reception optical fiber.
FIG. 9 schematically illustrates a primary part of such a conventional optical system unit for optical transceiver. The conventional optical system unit for optical transceiver 101 may be coupled with two or more connectors 102. The connector 102 is joined with one end of a transmission fiber optic cable 103 and one end of a reception fiber optic cable 104. The optical system unit for optical transceiver 101 includes a transmission lens 107 located opposite to and spaced by a certain distance from the end of a transmission optical fiber 106 accommodated in the transmission fiber optic cable 103 of the connector 102. Similarly, it includes a reception lens 109 located opposite to and spaced by a certain distance from the end of a reception optical fiber 108 accommodated in the reception fiber optic cable 104. Provided on the other side of the lenses 107 and 109 opposite to the connector 102 side is a lead frame 111. A light emitting diode 112 and a photo diode 113 are mounted on the lead frame 111 to face the transmission lens 107 and the reception lens 109 respectively.
In FIG. 9, the connector 102 is illustrated as a single unit. It is understood that the optical system unit 101 for optical transceiver when coupled with two or more of the connectors 102 includes a corresponding number of such optical systems.
As the connector 102 is joined with the two fiber optic cables 103 and 104, the conventional optical system unit for optical transceiver 101 is relatively large in the overall size. This allows the transmission lens 107 and the reception lens 109 to be used of large size. Also, this permits the light emitting diode 112 and the photo diode 113 to be generously spaced from each other, thus improving the separation between a transmission signal and a received signal.
However, as its connector 102 is large, the conventional optical system unit for optical transceiver 101 becomes bulky in the dimensions. As compared with the LAN cable joined hub as a like unit for transmission and reception of electric signals, the conventional optical system unit for optical transceiver 101 may be too large. It is hence proposed to provide a modified optical system unit for optical transceiver which can be coupled with a smaller connector accompanied with a single fiber optic cable for transmission and reception of optical signals.
FIG. 10 is an enlarged view showing schematically a modified optical system unit for optical transceiver coupled with one end of the fiber optic cable. The fiber optic cable 121 includes a transmission optical fiber 122 and a reception optical fiber 123 joined closely to each other by a distance L. The distance L may be as short as 0.75 mm. As a result, a connector 124 joined with the fiber optic cable 121 can be decreased to a size equal to that of the common LAN cable connector for electric signals. Consequently, the modified optical system unit for optical transceiver 125 coupled with the connector 124 will be minimized in the size.
However, when the distance L between the two optical fibers 122 and 123 is very small, their corresponding lenses 126 and 127, the light emitting diode 128. and the photo diode 129 may hardly be aligned with the two optical fibers 122 and 123. For compensation, a group of mirrors 131 to 134 are utilized to separate the two optical paths 135 and 136, denoted by the one-dot chain lines, from each other in directions orthogonal to the axes of the optical fibers 122 and 123 as shown in FIG. 10. Such a technique is disclosed in xe2x80x9cOpto-comxe2x80x9d, pp. 60, April 1998.
As the modified optical system unit for optical transceiver 125 shown in FIG. 10 includes the mirrors 131 to 134 for transmitting and receiving a pair of optical signals, its price will unfavorably be increased. Accordingly, some attempts for forming the lenses and the mirrors integrally by molding of an optically transparent material have been proposed. One of the attempts is depicted in the Electric Components and Technology Conference 1998 proceeding, xe2x80x9cLow Wave Length Transparent Epoxy Mold Optical Data Linkxe2x80x9d by Ichiro Tonai et al.
FIG. 11 is a view of the connector coupling end of such a modified optical system unit for optical transceiver described in the above proceeding, seen from the connector side. FIG. 12 is a cross sectional view of the modified optical system unit for optical transceiver 101 taken along the line Axe2x80x94A of FIG. 11 vertical to the sheet of paper. As shown in FIG. 12, the optical system unit for optical transceiver 141 is coupled with a connector 142.
The connector 142 shown in FIG. 12 is joined with a two-core fiber optic cable 145 having a transmission optical fiber 143 and a reception optical fiber 144. The connector 142 has two M type ferrule positioning holes 146 and 147 provided in the front side thereof. When its M type ferrule positioning holes 146 and 147 are in engagement with a pair of corresponding M type ferrule positioning pins 148 and 149 mounted at the opposite positions on the front side of the optical system unit for optical transceiver 141, the connector 142 is correctly coupled with the optical system unit for optical transceiver 141.
The optical system unit for optical transceiver 141 incorporates a resin body 151 in which the two M type ferrule positioning pins 148 and 149 are implanted. In the resin body 151, each of the opposite position of the transmission optical fiber 143 and the reception optical fiber 144 project hemispherically, and the resin body 151 construct the convex lens 152 and 153, respectively. The resin body 151 is made of a transparent resin material which is transparent for both a mode of light transmitted to the transmission optical fiber 143 and a mode of light received from the reception optical fiber 144. Also, a lead frame 155 of a sheet form is embedded in the resin material 151 to extend on a plane orthogonal to the M type ferrule positioning pins 148 and 149. A light emitting device 156 for emitting light via the lens 152 to the transmission optical fiber 143 is mounted on the lead frame 155 to face the transmission optical fiber 143. Also, a light receiving device 157 for receiving light transmitted via the lens 153 from reception optical fiber 144 is mounted on the lead frame 155 to face the bet reception optical fiber 144. The light emitting device 156 is connected by a wire 161 to a transmission signal line 158 which is provided flush with the lead frame 155. Similarly, the light receiving device 157 is connected by a wire 162 to a reception signal line 159 which is provided flush with the leaf frame 155.
In the optical system unit for optical transceiver 141 having the above arrangement, both the light emitting device 156 and the light receiving device 157 are mounted on the single lead frame. Accordingly, the distance from the light emitting device 156 to the end of the fiber optic cable 145 is equal to that from the light receiving device 157. In practice, the light emitting device 156 and the light receiving device 157 may commonly be different from each other in the optical characteristics including the size of the light transmitting or receiving area. For compensation, the two convex lenses 152 and 153 are separately designed and fabricated for giving optimum effects to different focal length or aberration.
The modified optical system unit for optical transceiver 141 shown in FIGS. 11 and 12 allows the light emitting device 156 and the light receiving device 157 to be aligned with the transmission optical fiber 122 and the reception optical fiber 123 respectively, thus eliminating the mirrors which are essentially provided in the previous optical system unit for optical transceiver 125 shown in FIG. 10. Also, as its lenses are fabricated by molding of a resin material, the optical system unit for optical transceiver 141 will be improved in the cost down.
However, the optical system unit for optical transceiver 141 shown in FIGS. 11 and 12 has the transmission optical fiber 122 and the reception optical fiber 123 spaced from each other by the distance L which is as short as 0.75 mm similar to that shown in FIG. 10. Accordingly, because the two convex lenses 152 and 153 formed integral with the resin body 141 by the molding process are very small in the size, their dimensional accuracy enough to have desired lengths of the focal distance may hardly be feasible.
The reduction of the number of components by molding the resin material may be achieved with the system unit shown in FIG. 10. More particularly, while the two lenses 126 and 127 are formed as a pair of arcuate projections as shown in FIGS. 11 and 12, the mirrors 131 to 134 are implemented by facets exposed to the air. As a result, those optical components are formed in a single unit. Accordingly, the lenses will no more be fabricated separately and the optical system unit for optical transceiver will be reduced in the production cost. It is however true that the resin material expands or contracts as the temperature changes. In case chat the mirrors are formed on facets tilted at a certain angle, any change in the ambient temperature ranging from xe2x88x9240 to +85xc2x0 C. may generate angular variation or distortion on the tilted facets. Consequently, the optical system unit for optical transceiver 125 shown in FIG. 10 can be formed by molding the resin material but with an unfavorable level of the optical characteristics.
It is thus an object of the present invention to provide an optical system unit for optical transceiver which is so formed integral with lenses by molding of a resin material as to exhibit a favorable level of the optical characteristics with no use of mirrors.
According to claim 1 of the present invention, an optical system unit for optical transceiver is provided comprising: (a) a transmission lens and a reception lens formed of an optically transparent resin material to project at the distal end of an arcuate contour towards and locate in front of one end of a transmission optical fiber and one end of a reception optical fiber respectively which are spaced by a certain distance from each other and accommodated in a single fiber optic cable; (b) a lead frame provided in the optically transparent resin material and formed by bending to have two steps so that the distances of the two steps along the axes of the optical fibers from the one end of the transmission optical fiber and the one end of the reception optical fiber respectively are different; (c) a light emitting device provided in the optically transparent resin material as located on one step of the lead frame to face the one end the transmission optical fiber; and (d) a light receiving device provided in the optically transparent resin material as located on the other step of the lead frame to face the one end the reception optical fiber.
As defined in claim 1, the transmission lens and the reception lens are formed integrally by a resin material which is transparent for the applied wavelengths of light so as to face the transmission optical fiber and the reception optical fiber respectively of a fiber optic cable and the distance between the light emitting device and the light receiving device is determined on the basis of the optical characteristic of the two lenses. Accordingly, the optical system becomes simpler in the arrangement with no use of mirrors. In addition, the transmission lens and the reception lens can commonly be used as are identical in the optical characteristics and the data of conventional similar lenses can be utilized for designing. This will facilitate the designing process of the system unit hence contributing to the speed-up and the cost down of the development and manufacturing. Moreover, as no mirrors are used, the system unit will remain stable regardless of changes in the ambient temperature. The single lead frame is bent to such a shape that the bent can successfully shield unwanted components of the light emitted from the light emitting device. Also, the difference in the distance to the lens between the light emitting device and the light receiving device can easily be controlled by varying the angle of bending the lead frame.
According to claim 2 of the present invention, the optical system unit for optical transceiver defined in claim 1 is modified in which the lead frame has rows of perforations provided therein along the bending lines so that the distances of the steps can be adjusted by varying the angle of bending.
As defined in claim 2, the lead frame according to claim 1 has the rows of perforations provided therein along the bending lines. Accordingly, the light emitting device and the light receiving device mounted on the lead frame are free from excessive stress developed during the bending process and can thus be prevented from unwanted physical damage.
According to claim 3 of the present invention, an optical system unit for optical transceiver is provided comprising: (a) a transmission lens and a reception lens formed of an optically transparent resin material to project at the distal end of an arcuate contour towards and locate in front of one end of a transmission optical fiber and one end of a reception optical fiber respectively which are spaced by a certain distance from each other and accommodated in a single fiber optic cable; (b) a first lead frame and a second lead frame provided in the optically transparent resin material and located so that their distances along the axes of the optical fibers from the one end of the transmission optical fiber and the one end of the reception optical fiber respectively are different; (c) a light emitting device provided on the first lead frame to face the one end the transmission optical fiber; and (d) a light receiving device provided on the second lead frame to face the one end the reception optical fiber.
As defined in claim 3, the transmission lens and the reception lens are formed by the transparent resin material, which is transparent for wavelengths of light to be used, so as to face the end of the transmission optical fiber and the end of the reception optical fiber respectively of the fiber optic cable. The two, first and second, lead frames are embedded in the resin material so that the distance between the light emitting device and the light receiving device can be determined arbitrarily and separately depending on the optical characteristics of the two resin lenses. Accordingly, the optical system can be simple in the arrangement with no use of mirrors for reflecting the light. In addition, the transmission lens and the reception lens can commonly be used as are identical in the optical characteristics and the data of conventional similar lenses can be utilized for designing. This will facilitate the designing process of the system unit hence contributing to the speed-up and the cost down of the development and manufacturing. Moreover, as no mirrors are used, the system unit will remain stable regardless of changes in the ambient temperature.
According to claim 4 of the present invention, the optical system unit for optical transceiver defined in claim 3 is modified in which one of the first and second lead frames which is nearer to the one end of the optical fiber has a window-like opening provided therein for clearing the optical path to the light transmitting or receiving device mounted on the other lead frame.
As a result, the two lead frames can be placed one over the other. This will implement the spatial arrangement of the two lead frames readily and accurately in the molding process of the resin material.
According to claim 5 of the present invention, the optical system unit for optical transceiver defined in claim 4 is modified in which the other lead frame also has a window-like opening provided therein at the same position as of the opening of the nearer lead frame and a light receiving device of back-side reception type is mounted to the side opposite to the optical fiber facing side of the other lead frame with its light receiving surface oriented to face the one end of the optical finer across the two openings.
As defined in claim 5, the light receiving device of back-side reception type can be used having relevant terminals mounted on the side opposite to the light receiving side. The difference between the distance of the light emitting device to its corresponding lens and the distance of the light receiving device to its corresponding lens can be adjusted by controlling the thickness of the two lead frames.
According to claim 6 of the present invention, the optical system unit for optical transceiver defined in claim 3 is modified in which a shielding sheet made of a conductive material is provided between the first lead frame and the second lead frame for inhibiting the light receiving device from receiving unwanted components of the light emitted from the light emitting device and connected to the ground for eliminating electrical noises.
The shielding sheet is provided between the two, first and second, lead frames and connected to the ground for eliminating electrical and optical noises. Alternatively, besides the shielding sheet, one of the first and second lead frames may be bent at its end to protect the light receiving device from receiving unwanted components of the light from the light emitting device.
According to claim 7 of the present invention, an optical system unit for optical transceiver is provided comprising: (a) a transmission lens and a reception lens formed of an optically transparent resin material to project at the distal end of an arcuate contour towards and locate in front of one end of a transmission optical fiber and one end of a reception optical fiber respectively which are spaced by a certain distance from each other and accommodated in a single fiber optic cable; (b) a lead frame provided in the optically transparent resin material, arranged in parallel with a plane on which the axes of the transmission optical fiber and the reception optical fiber extend, and formed to such a shape that the distances of two portions of its upper edge from the one end of the transmission optical fiber and the one end of the reception optical fiber respectively are different; (c) a light emitting device provided on one portion of the upper edge of the lead frame with its light emitting surface oriented to face the one end the transmission optical fiber; and (d) a light receiving device provided on the other portion of the upper edge of the lead frame with its light receiving surface oriented to face the one end the reception optical fiber.
As defined in claim 7, the lead frame is arranged at a right angle to the orientation of the previous lead frames. Since one end of the lead frame becomes opposite to the end of the transmission optical fiber and the end of the reception optical fiber, the light emitting device and the light receiving device mounted on the lead frame are used of side emission type and of side reception type respectively. Accordingly, the light emitting surface and the light receiving surface of the devices can be set to face the transmission optical fiber and the reception optical fiber respectively.
According to claim 8 of the present invention, the optical system unit for optical transceiver defined in any of claims 1, 3, and 7 is modified in which the transmission lens, the reception lens, and the relevant components are provided two or more sets corresponding to a number of the fiber optic cables employed.
The optical system unit for optical transceiver is not only one applicable to a single fiber optic cable but also capable of coupling with two or more fiber optic cables. According to the present invention, the light emitting device and the light receiving device are favorably aligned with the optical fibers of each fiber optic cable without using the conventional optical system where the optical paths are distanced from each other as shown in FIG. 10. Therefore, the optical system unit for optical transceiver can be minimized in the overall arrangement.